From a small island in the Baltic Sea to the large tropical islands of Borneo and Madagascar, this book is a global tour of these natural, water-bound laboratories. The book draws upon the many islands on which fieldwork was performed to convey key themes in ecology. By exploring the islands' biodiversity as an introduction to general issues, the book helps us to learn how species and communities interact in fragmented landscapes, how evolution generates biodiversity, and how this biodiversity is maintained over time. Beginning each chapter on a particular island, the book reflects on field studies before going on to pursue a variety of ecological questions, including: What is the biodiversity crisis? What are extinction thresholds and extinction debts? What can the biodiversity hypothesis tell us about rapidly increasing allergies, asthma, and other chronic inflammatory disorders? The world's largest island, Greenland, for instance, is the starting point for a journey into the benefits that humankind acquires from biodiversity, including the staggering biodiversity of microbes in the ecosystems that are closest to us—the ecosystems in our guts, in our respiratory tracts, and under our skin. Conceptually oriented but grounded in an adventurous personal narrative, the book lifts the natural mysteries of islands from the sea, bringing to light the thrilling complexities and connections of ecosystems worldwide.